Submesoscale processes-induced vertical heat transport modulated by oceanic mesoscale eddies

Abstract

Oceanic submesoscale processes mainly arise from phenomena such as jets, density fronts, and mesoscale eddies. Previous studies suggest that the overall submesoscale processes transport heat vertically upgradient, i.e. from cold to warm. However, it is not clear whether the submesoscale processes-induced vertical heat transport (VHT) in mesoscale eddies remains upgradient. Therefore, the present study focuses on submesoscale-induced VHT modulated by mesoscale eddies. A high-resolution oceanic numerical model product is applied to examine the VHT induced by submesoscale processes associated with a pair of cyclonic and anticyclonic mesoscale eddies in the Kuroshio Extension (KE) region. Eddies at different time steps are collocated in terms of the eddy centers to reconstruct a time series of a new eddy dataset that presents eddy-modulated submesoscale processes. The frequency-wavenumber spectra, Rossby numbers, and strain rates in the pair of eddies reveal the existence of submesoscale motions surrounding mesoscale eddies. The variables are decomposed into monthly mean mesoscale and submesoscale components to calculate submesoscale VHT at low-frequency (LF) and high-frequency (HF). The results indicate that submesoscale VHT is modulated by mesoscale eddies mainly along the eddy boundaries. The LF submesoscale VHT (upward in both cyclonic and anticyclonic eddies) dominates the monthly-averaged submesoscale VHT. The magnitude of the hourly HF submesoscale VHT is larger than the LF component, while its monthly average becomes negligible because it is caused by periodical internal waves. The submesoscale VHT along the eddy edges is related to strong frontogenesis which develops the vertical flux.